Positive interlocking safety switch



y 1, 19 68 R. H. FIELD ETAL 3,383,985

POSITIVE INTERLOCKING SAFETY SWITCH Filed July 31, 1967 SOURCE l3a to initiator Fig.2 2. 26. CD

l0 I f '5 i 5 I4 25 i ;--25

l l 28 f- CHAMBER |3b Fig.3

INVENTORS: RICHARD H. FIELD CHARLES T. DAVEY RAYMON G. AMICONE ATTORNEYS United States Patent ()ffice 3,383,985 Patented May 21, 1968 ABSTRACT OF THE DISCLOSURE A firing chamber housing interlock apparatus having safety switch means which prevents the housing door from being opened while a test is being conducted or until the test device is grounded. A latch plate whose movement is controlled by the opening and closing of the chamber door is held in place until a proper plug connection is made with an associated plug receptacle.

Background of the invention This invention relates to a firing chamber safety switch, and particularly, to an interlock safety switch mechanism associated with a housing providing a firing chamber which provides both mechanical and electrical interlocking to insure protection for operating personnel while an exposive device is being tested.

The need for a reliable device designed to insure complete protection against haphazard operation while testing initiators, or other like explosive devices in a firing chamber has presented a great problem to test technicians and engineers for a considerable period of time.

The safety interlocked firing chamber of the present invention is directed to solving this important problem to a degree no existing device had been able to accomplish. That is, complete protection for the operating personnel conducting detonation tests by insuring both mechanical and electrical interlocking of the firing chamber housing and each device being tested.

Summary of the invention In general, the inventive apparatus comprises .an improved firing chamber safety switch which overcomes certain recognized disadvantages of the prior art and provides a completely reliable and safe method for testing dangerous explosive devices.

The inventive apparatus includes among its operational elements, -a roller actuator fixedly attached to the door .of a housing providing a firing chamber or other similar testing inclosure means. In close proximity to the actuator, which is attached to the movable edge of the door is a switch box and supporting bracket assembly which provides electrical plug receptacle means and houses a mechanical interlocking switch mechanism of the said apparatus.

The plug receptacle permits .only two possible connections therein by a companion plug-in-unit having contacts for electrical connection therewith. One receptacle connection is adapted to connect the device under test with a power source, or other external electrical equipment, to initiate and permit the test to run to completion. The other receptacle connection is adapted to ground or short circuit a device under test so that it will not prematurely explode when the door is opened.

The mechanical interlocking mechanism is in contact with the roller actuator afiixed to the housing door and prevents the door from being opened until the receptacle ground connection is made. The interlock mechanism also prevents the receptacle power connection from being made until the door is closed, thereby insuring protection for personnel conducting the test from a misfire or any other haphazard operation of the test device.

Brief description of the drawings In the drawing, 'FIG. 1 is a top view, in diagrammatic form, of an explosive firing chamber and an interlocking safety switch therefor embodying the invention,

FIG. 2 is a side view of a manual plug-in-unit used in conjunction with the safety switch as shown in FIG. 1, and

FIG. 3 is a front view of the firing chamber and associated switch elements as shown in FIGS. 1 and 2 further showing their operative relation in accordance with the invention.

Description of the preferred embodiment The invention may be more fully understood by recourse to the drawing, wherein like reference numerals apply to like parts throughout. Referring now to FIG. 1 of the drawing, a rectangular housing 10, having a suitable firing chamber therein, is provided for testing initiators or other like explosive devices. A movable loading door 11 is provided at the entrance to the firing chamber for opening and closing the same. The door is hinged to the housing at one edge (not shown) thereby making it movable wit-h respect to the opposite edge of the housing.

A switch box and supporting bracket assembly 12 is positioned in close proximity to the movable edge of the door, or it may be fixedly attached to the housing, as shown in FIG. 3 to which reference is now made, along with FIG. 1.

The switch box 12 provides for three evenly spaced receptacle contact'elements or plug apertures 13, 13a and 13b, mounted on its surface in axially-parallel relation to each other. Also provided on the surface of the panel are two safety pin receptacle contact elements 14 evenly spaced midway between the center contact element and the outer two elements. The dimensional configuration of the receptacle contact elements on the panel 12 permits only two possible connections to be made when the plugin-unit shown in FIG. 2 is used, as will subsequently be discussed.

Fixedly attached to the door 11 near its movable edge is roller actuator 15 which extends a distance past the edge. In contact with the roller actuator is a T-shaped latch dog 116. The latch dog is connected or pinned to the rear surface of the panel 12 at the intersection of its two extremities, shown at 17, so it is capable .of being rotated about that point by the movement of the roller actuator when the door is opened. The latch dog is initially positioned with respect to the roller actuator 16 so that when the door is opened the latch dog will be rotated about its common axis for and when the door is subsequently closed the latch dog will be returned to its initial starting position. The edge of the roller actuator which is in contact with the latch dog is preferably circular in shape to insure a smooth camming action there with, but may be fiat or any other shape which will produce a similar contact and motion.

A latch plate .18 is connected to the latch dog through a bar link 19. The bar link is pinned to the latch dog as indicated at 20, and to the latch plate as indicated at 21, to allow for movement of the latch plate in a direction away from the housing 10 when the door 11 is opened and latch dog 16 is caused to rotate.

The latch plate 18 is a substantially fiat U-shaped structure whose initial position, that is, when the door .11 is in its closed position, is in a plane below and parallel to the plane which the outer top surface of panel 12 defines. The outer edges of the latch plate, that is, the ends of the legs of the U-structure, are initially adjacent to and slightly below the safety pin contact elements 14. The width of each extremity of the latch plate which forms the U-shape structure are slightly wider than the circumference of the safety pin contact elements.

Attached to the side wall of the inner surface forming panel 12 is a lock bar 22. The lock bar extends beneath and into alignment with said safety pin contact element in the same plane as latch plate 18 and is in juxtaposition therewith, contacting and securing said latch plate in its initial position. Because of the barrier to movement prescnte by the lock bar, the door 11 is also unable to be opened because the latch dog 16 is in contact with the roller actuator which is also unable to move. The lock bar is attached to the panel 12 by means of a spring loaded mechanism which permits the bar to be moved downward and out of its locking position thereby allowing the housing door to be opened. This operation will be more fully explained in conjunction with FIG. 2, to which reference is now made.

FIG. 2 shows a manual plug-in-unit which is used with the interlock mechanism shown and described in FIGS. 1 and 3. The plug-in unit is provided with two plug contact elements which are electrically connected to each other and present a jumper plug, as shown by a shorting or connecting wire 26. A safety-pin plug contact element 27 is placed midway between the plug elements 25 and in line therewith. A groove or neck 28 is machined out of the circumference of the plug element 27. The necessity for this will become evident when the operation of the interlock mechanism is more fully explained.

The dimensional configuration of the plug elements 25 and 27 permit connection to be made between either of the outer receptacle contact elements 130 or 1311 and the center receptacle element 13. A hand grip 29 is attached to the plug-in-unit to facilitate the making or breaking of the above two possible connections, or positions.

The center receptacle element 13 is adapted to be electrically connected to the explosive device to be tested in the housing firing chamber and the receptacle element 13a is adapted to be connected to an external power source (not shown) which is of sufficient potential to initiate the explosive device. Therefore, when the manual plug-in unit shown in FIG. 2 is made to connect receptacle elements 13 and 13a, power to initiate the explosive device is provided thereto.

The receptacle element 13b is adapted to be connected to ground or to a source of potential or may be adapted to be electrically connected to the receptacle element 13. Therefore, when the manual plug-in unit is made to connect elements 13 and 13b, an electrical ground or short is provided on the elements and the explosive device cannot be initiated.

The mechanical operation of the inventive device will now be more fully considered. With no plug connection having been made, the door 11 cannot be opened because of the barrier provided by lock bar 22. The door may be opened only when the manual plug-in unit is connected to provide the safety ground connection. Once this connection is made the device under test is grounded so that no misfire can occur and the safety pin plug element 27 contacts the spring loaded lock bar, depressing the lock bar sufficiently enough to free the latch plate for movement. A V-shaped notch 23 is provided on the end of the leg of the latch plate that is in contact with the lock bar so as to allow for the necessary movement to enable the door to be fully opened.

When the door is opened the movement of the roller actuator 15 against the latch dog 16 rotates the latch dog 90 which in turn moves the latch plate, whereby its notched edge 23 fits into the grooved circumference 38 of the safety pin plug element 27. Thus, the plug-in-unit is locked into place until the door is closed and the latch plate is retracted and returned to its original position.

The other extremity of the latch plate is also moved into operating a position directly below and covering the other of the safety pin receptacle elements 14. This operates to prevent any possible power connection from being made and provides a second insurance feature if the interlock mechanism fails to lock the plug-in unit in place.

When the door is closed the latch dog returns through and retracts the latch plate. This action unlocks the manual plug-in unit and uncovers the upper safety pin receptacle contact element. Removal of the plug-in-unit permits the spring loaded lock bar to rise and secure the latch plate. Connection can now be made to the power receptacle contact element 13a.

Should a misfire of the explosive dvice under test occur, the plug-in unit can be removed from the power position. However, the door cannot be opened until the plug is returned to the ground or shorting position, thereby depressing the lock bar and releasing the latch plate. The motion of the door again returns the latch dog through 90 and the interlock sequence is complete.

FIG. 3 shows the switch box assembly 12 of the inventive apparatus fixedly mounted to the firing chamber housing 10. The roller actuator 15 attached to the door 11 is shown contacting the latch dog 16, with the remaining apparatus fully enclosed by the switch box 12. The switch box is shown positioned to face to the front of the housing, but this is shown merely by way of example. The switch box may be mounted to face to the top of the housing or it may be placed in a fixed position in close proximity to the housing, its positioning depending on the shape of the housing, and the needs of the personnel conducting the tests.

While the invention has been shown and disclosed with reference to a firing chamber safety interlock switch using a three contact element system, it is obvious that it may be applied to provide a safety interlock on a vacuum chamber or other like device which may need to employ a six contact element version.

The significant aspects of the interlocking mechanism of the present invention involve the mechanical and electrical interlocking that is provided. The housing door can only be opened when the manual plug-in-unit is in the set of receptacles to provide an electrical ground or short on the device to be tested. The plug-in-unit cannot be pulled out when the door is open; the door must be closed and then the plug can be inserted into the receptacle contact elements that are adapted to provide connection for the test device to an external power source.

There is claimed:

1. A safety-interlocked firing chamber for explosives, comprising in combination, a rectangular housing providing an internal firing chamber, a movable loading door for opening and closing said chamber, said door being movable with respect to one outer edge of said housing, a roller actuator fixedly attached to said door and extending therefrom near said one edge of the housing, a switch box providing a plug receptacle having a plurality of spaced receptacle contact elements permitting two possible plug connections therewith and fixedly attached to said one edge of said housing in close proximity to said roller actuator, a manual plug-in-unit capable of making either of said plug connections, and a safety-interlock means enclosed in said receptacle and in contact with said roller actuator, said interlock means being operative to prevent the opening of said door until one of said plug connections is made, and being further operative to prevent the other of said plug connections from being made until said door is closed.

2. A safety interlocked firing chamber for explosives as defined in claim 1, wherein said plug receptacle includes three receptacle contact elements aligned in equally spaced axially-parallel relation and tWo safety pin receptacle contact elements equally spaced one on each side of the center receptacle contact element, said center and one other receptacle contact element providing connections for external power circuits, and said center and the remaining receptacle contact element providing a grounding connection.

3. A safety interlocked firing chamber for explosives as defined in claim 2, wherein said manual plug-in unit comprises two axially aligned electrically connected plug contact elements and a centrally located safety pin plug contact element adapted for cooperative plug-in connection with either of said safety pin receptacle contact elements and a pair of said receptacle contact elements on either side of the selected safety pin element, thereby to provide said two possible plug connections.

4. A safety interlocked firing chamber for explosives as defined in claim 3, wherein said safety-interlock means comprises a lock bar fixedly attached to the switch box opposite the housing and extending into alignment with the safety pin receptacle contact element between the receptacle contact elements providing a grounding connection, a substantially U-shaped latch plate having an end of one leg thereof positioned to contact said lock bar with the door closed thereby temporarily preventing said door from being opened, a latch dog in contact with said actuator and capable of being rotated 90 about a stationary point when the door is opened and which is returned 90 to its initial position when said door is closed, a bar link connecting said latch dog and said latch plate whereby said plate is movable toward and in the plane of said lock bar when said door is opened and said latch dog is rotated, said lock bar capable of being depressed by said safety pin plug element with the plug-in unit inserted into the receptacle contact elements providing a grounding connection, whereby said latch plate is free to move thereby allowing said door to be opened.

5. An interlocking safety switch mechanism for use with a housing having an internal firing chamber and a movable loading door therefor in one wall of the housing, comprising in combination, a roller actuator fixedly attached to the movable edge of said door and extending a distance outward therefrom, a T-shaped latch dog capable of being rotated about an axis through the point of intersection of its legs and positioned so that said roller actuator makes contact therewith, whereby when said door is opened or closed said latch dog is rotated 90, a substantially flat U-shaped latch plate having a V-shaped notch in the end of one leg thereof, a bar link connecting said latch dog and said latch plate whereby said plate is slidably movable in response to rotation of said latch dog, a switch box attached to said housing in close proximity to the movable edge of said door, said switch box including a plug receptacle having three evenly-spaced axiallyparallel plug-apertures and two interposed smaller safetypin apertures in line therewith, a manual plug-in unit having two electrically connected terminal-plugs and an interposed central safety pin adapted for cooperative plug-in connection selectively with either of said pin apertures and a pair of said plug apertures on either side of the selected pin apertures, thereby to provide only two operating positions in connection with said plug apertures, and a spring loaded lock bar one edge of which is fixedly connected to said panel at the edge opposite said housing and positioned to extend into alignment with one of said safety apertures for engagement by a safety pin thereon, said latch plate being moved with the door in the closed position to engage said lock bar at said notched leg and hold the door in said closed position, and said lock bar being adapted to be depressed by insertion of a safety pin of said plug-in unit in said one of the safety-pin apertures and to release said latch plate to move and permit said door to be opened.

6. An interlocking safety switch mechanism as defined in claim 5, wherein the notched edge of said latch plate is adapted to contact the safety pin of said plug-in unit with said door in the open position and thereby to lock said unit in one of said operating positions, and said latch plate further being adapted to retract in response to movement of the door to the closed position, thereby to unlock said unit for removal to the other of said operating positions.

7. An interlocking safety switch mechanism as defined in claim 6, wherein with the plug-in unit in position over one safety pin aperture, and wherein, the latch plate is movable to cover the other safety-pin aperture with the door in the open position thereby preventing any additional plug connections from being made with said mechanism.

8. An interlocking safety switch mechanism as defined in claim 5, wherein said receptacle is adapted to provide a test connection for external electrical equipment with the door closed and said plug-in unit in one of its operating positions, and wherein said receptacle is further adapted to provide a safety ground connection with the door open and the plug-in unit in the other of its operat ing positions.

9. The combination with a housing for explosive devices providing an internal firing chamber and having a movable loading door forming one wall thereof to open and close said chamber, of an interlocking safety switch mechanism therefor comprising, a receptacle attached to said housing adjacent to the movable edge of said door for receiving a jumper-plug connection therewith, a jumper plug adapted to provide said connection in two operating positions thereon, one of which provides an external electrical circuit connection for said mechanism and the other of which provides a safety ground connection therefor, actuator means afiixed to said chamber door adjacent to said movable edge, and safety interlock means contacting said actuator means and enclosed by said receptacle, said safety interlock means being operable to prevent the door from being opened in the absence of said jumper plug from said receptacle, and said safety interlock means further being operable to prevent the jumper plug from being connected with the receptacle in the said one operating position with the chamber door withdrawn from the closed position.

References Cited UNITED STATES PATENTS 2,469,400 5/1949 NeWell 89-135 X 2,762,267 9/1956 Persson et al 89-135 2,898,812 8/1959 Meyer 89135 SAMUEL W. ENGLE, Primaly Examiner. 

